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Wi-Fi over Coax
- k33n 7y agoIs this just coax as backhaul? Or is signal actually emanating from the shielded coax cable? I haven't had my coffee yet.
- pjc50 7y agoIt's sticking the Wifi antennas at the end of a long cable. A "feedline" in the usual terminology. How this interacts with beamforming and antenna diversity is .. not specified. The basic idea seems simple enough: rather than stick an AP on one side of a wall and accept a 15-20dB loss through the wall, or use two APs, cable one antenna through the wall so the AP has a clear line of sight on both sides of the wall.
- chrismeller 7y agoThat was my interpretation as well. I feel like this is another case of someone new to the industry creating a “standard” for something that, had they been around for a few decades, they would have realized already existed in a different context. Case in point: we have had “external” uni- and omni-directional antennas, even for plain old 802.11, for decades.
- Sharlin 7y agoIsn't this exactly reusing old technology that has existed for decades (well, over a century now) in a slightly different context? I mean, a lot of pre-existing coax is there exactly for the purpose of running a signal between an antenna and a device…
- chrismeller 7y agoOf course. But would you call that “WiFi over coax”? No one I knows would...
- vvanders 7y agoHonestly if I'm running a cable I'd rather run PoE over RJ45 and just have a second AP. PoE powered APs are cheap enough these days.
- deleted 7y ago[deleted]
- OJFord 7y agoNo I think it's like running a (coax, as well) cable to the television antenna on your roof instead of having rabbit ears sticking out of the back of the box.
- preek 7y agoSo.. WiFi cables do exist? I feel a little bit bad about some discussions I’ve had over the years. They could have even been more complicated(;
- EarthIsHome 7y agoDefining it as a Wi-Fi cable is a bit narrow. It's just a coaxial cable between an antenna and the router. Just make sure your cable is matched to your antenna and using the correct connectors.
- dboreham 7y agoAnd an attenuator.
- EarthIsHome 7y agoWhile technically correct, using a coax cable will reduce some dominating loss factors like multipath loss, free-space path loss, and line-of-sight loss. So, in reality, your link might improve.
- himinlomax 7y agoYou'd only need an attenuator if you're connecting two WiFi adapters directly through coax. In what is discussed here, waves always travel through the air at some point, which does the attenuation.
- burtonator 7y agoWired wireless ... what are you confused about? :-P Combine this with power over IP and you're SET!
- dylan604 7y agoOr IP over power
- 7y ago
- mjlee 7y agohttps://en.wikipedia.org/wiki/Leaky_feeder https://en.wikipedia.org/wiki/Leaky_feeder might be interesting too - essentially using a cable to act as the actual antenna.
- EarthIsHome 7y agoThis is just extending the antennas using 50-ohm cables. By using couplers and multiple cables, you can connect multiple antennas to the same access point. It's a way to physically separate the antennas from the router by using a coax cable.
- q3k 7y agoHome TV coax has a characteristic impedance of 75ohm. If you just plug consumer devices in directly you will get a pretty significant SNR loss from reflections and other impedance mismatch effects.
- EarthIsHome 7y agoSure. But I would bet that most Wi-Fi access points use a 50-ohm system. (Plus, the connectors on a home tv coax cable probably won't mate with the router connectors.) If you want to use a 75-ohm cable, you'll have to use impedance converters to convert to 50 ohms. Bottom line: just make sure the components you're connecting in your system are properly matched to avoid a lot of reflections and power loss.
- kazinator 7y ago> If you want to use a 75-ohm cable, you'll have to use impedance converters to convert to 50 ohms. ... says the article, clearly.
- dboreham 7y agoThis confused me but I think you mean "Most WiFi Access Points use a..."?
- EarthIsHome 7y agoThanks! Corrected
- kps 7y agoDoesn't everyone have a stash of old 10base2 cables? The idea of running a network over them is strangely appealing.
- dfamorato 7y agoPardon my ignorance on the topic, but are there any commercially available (enterprise grade) products for Wi-Fi over Coax? If this is used for “back-haul”, what is the key differentiator between this and MoCa (or similarly Ethernet over Powerline)
- vvanders 7y agoWell if you want one difference this won't throw RF hash all over the spectrum like ethernet over powerline does.
- y04nn 7y agoAlso, modulation of light waves with radio signals to send them over fiber: https://en.wikipedia.org/wiki/Radio_over_fiber https://en.wikipedia.org/wiki/Radio_over_fiber
- friendlybus 7y agoSmall example https://hackaday.com/2018/10/19/wired-wireless-over-coax/ https://hackaday.com/2018/10/19/wired-wireless-over-coax/
- bob1029 7y agoI think it would be pretty awesome to inject the WiFi RF into the coax of my home from the distribution panel. I only use the 1 line for my Comcast internet and ethernet/wifi to connect everything else. All of those other coax lines to each room are sitting entirely unused right now... All you would need is a WiFi router that has a bunch of RG6 connectors on it. Wire in where the coax splitter/amplifier would normally live for CATV/satellite service. And then in each room where the coax feed ends up, simply screw on an antenna with matching RG6 connector.
- jpizza 7y agoThis is a very timely post for me. My contractor mentioned this to me last week. It caught me totally off guard and seemed counter intuitive to my knowledge of wifi connections. Pretty neat and thank you for sharing.
- mceachen 7y agoWouldn't it be more "future proof" to use something like cat7 rather than coax?
- snovv_crash 7y agoI think the idea is that if you already have coax pulled (eg for TVs), you can just connect it to a WiFi access point instead and put an antenna on the other side.
- jrockway 7y agoI think what Wifi-over-Coax is trying to get around is having to coordinate multiple access points. Wifi breaks down particularly horribly when some of the stations and APs can't hear each other. By only having 1 AP, you avoid some of that problem. (Of course, stations can still interfere with each other. So I'm not sure how useful this is in practice.)
- smitty1e 7y agoI'll bite: how is this superior to MOCA? https://en.wikipedia.org/wiki/Multimedia_over_Coax_Alliance https://en.wikipedia.org/wiki/Multimedia_over_Coax_Alliance
- punnerud 7y agoBy turning a Coax cable inside out you get a radiating cable. This is used now in every train tunnel in Norway to get good 4G coverage.
- hamtastic 7y agoThe possibilities here with sufficiently sophisticated software and tunable hardware (deep learning of RF propagation characteristics in a building using data from portable sensors) are fascinating! But honestly, MOCA already solves this problem. The MOCA 2.5 standard (https://en.wikipedia.org/wiki/Multimedia_over_Coax_Alliance#MoCA_2.5 https://en.wikipedia.org/wiki/Multimedia_over_Coax_Alliance#...) already delivers 2.5gbit total (time-multiplex) throughput which is more than enough for real-world no-compromise bidirectional gigabit ethernet on isolated runs or distributed backhaul to multiple wifi APs. I'm using this in my (115 y.o.) house now where new cable runs are impractical and the coax plant is unused.
- kevin_nisbet 7y agoI was thinking about this for a minute, I don't think this technology is valuable because MOCA already exists and can be used instead, I suspect it fits a sort of different use case. It allows antennas to be separately installed from the radios, and allowing existing coax cabling to be used for the distribution. So my read is instead of having to install power, MOCA, and various endpoints around, I can centrally install my radios/APs, and distribute the antennas if I have existing cabling, such as cabling for security cameras.
- tomatocracy 7y agoYes - that's been my experience with MoCA too. I needed to add an AP in one room and putting a new ethernet cable would have been a huge hassle. Luckily there was an existing TV extension into the room and a pair of MoCA adaptors works perfectly over the run. It's significantly better than Powerline options. The other option to be aware of is G.hn on 2-wire telephone extension cable (that wasn't relevant in my case) - the adaptors for this seem to be more expensive and harder to find though than MoCA.
- war1025 7y agoWhat hardware are you using? I looked briefly into this since I also have coax run throughout the house unused, but it was hard for me to know what to look for.
- js2 7y agoToo bad we ripped out all those 50-ohm cables years ago: https://en.wikipedia.org/wiki/10BASE5 https://en.wikipedia.org/wiki/10BASE5
- geocrasher 7y agoRunning 2.4ghz or 5.8ghz over run-of-the-mill coaxial cable will introduce a lot of losses. It'll have to be low loss stuff similar to LMR400 to really be useful, I'd think. This would only be feasible if such coax already exists. Otherwise it's cheaper to run multiple access points.
- globular-toast 7y agoI wasn't aware of coax usage other than for TV. I guess I assumed that twisted-pair cables were far superior for data transmission, but maybe not? I recently moved in to a home that has been pre-wired with Cat5 and also coax to each room. The wiring was left unterminated but I assumed the coax was just meant for TV reception. But I did discover there is a second coax cable that has been left unterminated at both ends and I wonder if this is meant for data? I really don't like not knowing but I'm unable to get hold of the people who did the wiring during lockdown!
- toast0 7y agoA typical satellite receiver has two or sometimes three coax connections to the dish (or to the inhouse distribution platform). They could have built for that. Or it's a spare pull in case the cable fails mid span. Or to be able to get cable + antenna. Or to be able to use a centrallized powered splitter for two uses at one location, which would be better than using another splitter in the room, but probably not needed.
- gte525u 7y agoIt could 10base2 which is Ethernet over coax. It used a different connector (BNC) than what cable boxes use.
- bcoates 7y agoEverybody hates punching holes in walls and running new cables, but this is almost certainly the wrong solution for almost every problem, outside of the weirdest of edge cases. For starters, you're going to lose MIMO, so you've substantially downgraded your network's ability to handle multiple clients. It's also really unlikely that your weird old coax system is clean and not a rat's nest of splitters and unterminated ends (=interference). Attaching multiple antennas to a single AP in a non-MIMO configuration is not a cost effective way of doing DAS with current technology, if it ever was. More, lower-powered APs all over the place is where you want to be spending your budget. If you want to save money on install, do PoE.
- dogma1138 7y agoEthernet over power line (basically DSL) has become quite good these days, you can get fairly cheap 1gbe units today and unless you have some really crappy wiring with noisy appliances they don’t have many issues.
- war1025 7y agoI looked into this pretty seriously about two weeks back when I realized that I'm losing about 2/3rds of my connection speed (30 Mbps at router) while sitting at my desk at home. I backed off for now because I wasn't sure how well it would work in practice and honestly the speeds I do get are perfectly fine for what I do. Curious if you or anyone else has recommendations on what I should be looking for / avoiding if I were to go that route and invest in some powerline ethernet equipment.
- Nextgrid 7y agoCan you actually find an Ethernet over power line adapter that delivers 1Gbps? From my experience you only get like a third of the advertised bandwidth.
- dogma1138 7y agoI get pretty much 80-85% of the advertised speed on my TPLink AV1300 just over 1 gig.
- acd 7y agoWifi over coax could have usage for trains. You would connect wifi access point to fibre from the ground. Wifi signal is output to coax cable running along side with the power lines or from the ground next to the track. Wifi is beamed into the train. Local Wifi access points spreads the wifi signal in the train.
- neilalexander 7y agoInterference would likely be a problem here, not to mention cost. Using 4G uplinks from the trains is likely significantly cheaper.
- EquallyJust 7y agoSome automated train systems already do this for control such as some of the Vancouver SkyTrain lines. From the SelTrac wikipedia page: "in newer versions of SelTrac, the control signal is transmitted inside the running rails at radio frequency using IEEE 802.11 (WiFi) access points. " https://en.wikipedia.org/wiki/SelTrac#Communication https://en.wikipedia.org/wiki/SelTrac#Communication
- segfaultbuserr 7y agoWhat the article didn't mention is the possibility to build a "wired wireless" network using leaky feeder [0]. Unlike a normal coax feedline, a leaky feeder is a special coax feedline that is designed to leak a bit of RF along its way, thus providing wireless coverage on everywhere the coax runs. It's useful in areas when using antennas at fixed points is difficult to provide a throughout coverage, such as a building complex or a tunnel. [0] https://en.wikipedia.org/wiki/Leaky_feeder https://en.wikipedia.org/wiki/Leaky_feeder
- rwmj 7y agoIt's how they recently "wired" the London Underground for 4G. https://www.wired.co.uk/article/london-underground-4g https://www.wired.co.uk/article/london-underground-4g
- OrangeMango 7y agoBack in the day, almost all cell phones had a miniature coax port on them. They were "hidden" in that you probably had to pry off some nondescript part or open the battery cover up or something. This is how we tested mobile networks. It works great. The only problem is when someone forgets to make a tight connection or attach a signal attenuator. Since the first thing you always test is emergency calls, once in a while your call ends up on the real mobile network and the fire department shows up in your parking lot. This happened about once or twice a month where I worked. They knew what our business was so they were never mad at us, but we had to pay a fine each time.
- dogma1138 7y agoIt’s not only how they tested mobile networks. The old Nokia and Ericsson phones as well I think as some Motorola’s had a rubber plug in the back just below the external antenna with a coax port that you had to remove when you plugged the phone into the a car speaker phone system the phone would then hook to an external or a larger antenna glued to the windshield.
- OrangeMango 7y agoInteresting, that must be why the coax port survived from engineering to production.
- dogma1138 7y agoThe external port was a requirement for kits like this https://images-na.ssl-images-amazon.com/images/I/411PQXERG6L._AC_.jpg https://images-na.ssl-images-amazon.com/images/I/411PQXERG6L... But signal testing kits also used it. This survived until 2G the 5110 still had it. When 3G came out the coverage was good enough and I’m guessing that issues with signal strength in cars was more or less solved.
- ThePowerOfFuet 7y agoWhat a blast from the past... I remember installing that exact kit (plus antenna) in my own car some twenty years ago. It worked great.
- rietta 7y agoI'm struggling to see how this is anything but using feed lines to the antenna. We've done this for decades to attach rooftop high gain antennas to an equipment closet or if you are a HAM radio operator and want to have an outdoor antenna while your rig remains inside. If this were node-to-node, doesn't this just fit the definition of old school ethernet over coax?
- pmorici 7y agoIt is easier and cheaper to use 50ohm compatible WiFi when dealing with situations like trying to communicate with equipment inside an enclosure through a slip ring.
- rubatuga 7y agoI'm curious to know, at what frequency in a pair of wires is it considered to be EM waves travelling through it? I know that Ethernet is changing voltage (electric field) at frequencies of ~30MHz, while WiFi travelling through a pair is an EM wave at a frequency of 2.4 GHz. At what point does it change to EM?
- ac29 7y agoWouldnt any wire with electric charges in motion be considered to have EM waves? I dont think there is a minimum frequency per se, at least not a relevant one.
- rubatuga 7y agoWell to counter that point, wifi has to go through coax so that the EM waves it creates don't induce current in nearby conductors. But for a standard Ethernet (100Mbit) cable, i.e. unshielded pair, you can place it right up against metal if you like.
- guenthert 7y agoUnshielded twisted pair. Try the same with straight conductors ;-)
- rubatuga 7y agoGot it! Ethernet uses balanced pairs, which by themselves have some form of common mode rejection, but twisting it greatly reduces the harmful effects in the case where one conductor is closer to the EM interference. Twisted balanced pair has a lot of loss at >1GHz, at which point using a confined EM space in a coaxial cable can help prevent that. Ethernet stays under 250MHz, while WiFi is >2.4GHz, hence the cable differences. As another parent mentions, all changing currents produce EM waves, it's just the losses are much more important as the frequency increases. The following page helped me understand it as well. https://ham.stackexchange.com/questions/6445/why-isnt-twisted-pair-used-for-feedlines https://ham.stackexchange.com/questions/6445/why-isnt-twiste...
- LockAndLol 7y agoThat article is only written for experts. It'd be great if someone here that understands what it's actually about could update the article and contribute a better description for the laymen.
- pedrocr 7y agoThe article mentions 802.11r for fast roaming between APs and how this avoids it. I've seen mentions of networks where the APs just forward WiFi packets and a central router does all the actual negotiation to achieve the same effect. It's too bad something like OpenWRT doesn't include it.
- garaetjjte 7y agoAlternatively you can use HomePlug protocol over coax cabling. (HomePlug is normally used to Ethernet-over-mains) Instead of buying complete mains units there also smaller modules too, eg. LX200V20
- dusted 7y ago10base2: https://www.youtube.com/watch?v=82E7vhtLxNs&t=9 https://www.youtube.com/watch?v=82E7vhtLxNs&t=9
- tomasGiden 7y agoEricsson has something similar for cellular signals over CAT5 called Ericson Dot [0]. Though I believe they have it at baseband or intermediate frequency in the cable and then shift it up in the Dot. Disclosure, I worked at Ericsson when the first Dot was released, but never with it myself. But they were really proud of it I remember. [0] https://www.ericsson.com/en/portfolio/networks/ericsson-radio-system/radio/indoor/radio-dot-system https://www.ericsson.com/en/portfolio/networks/ericsson-radi...